Patients with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, may be an exception to the rule that being overweight is a health hazard. Massachusetts General Hospital (MGH) researchers found that ALS patients who were mildly obese survived longer than patients who were normal weight, underweight or even overweight. The study will appear in the journal Muscle & Nerve and has been published online.

“We have long known that being underweight shortens survival for ALS patients,” says senior author Anne-Marie Wills of the MGH Neurology Clinical Trials Unit. “We were surprised to find that increased body mass index, or BMI, increased chances of survival.”

The MGH team analyzed data on more than 400 patients who had participated in three clinical trials of potential ALS drugs. As expected, the shortest survival was seen in malnourished or morbidly obese patients, but patients in the mildly obese range had the longest survival of any BMI group.

“While this finding needs further investigation, we hypothesize that it is due to increased energy reserves available to these patients,” says Wills, an instructor of neurology at Harvard Medical School. “We don’t know whether actively putting on weight would be helpful, but right now I’m telling my patients with ALS they can eat anything they want.”